Psoriatic Arthritis — SCE Rheumatology MCQ
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Correct answer: E — Preferential inhibition of JAK1 signalling
Upadacitinib is an oral, selective and reversible Janus kinase inhibitor that preferentially inhibits signalling mediated by JAK1 or JAK1/3, with functional selectivity over cytokine receptors signalling through JAK2 pairs. Therefore, preferential inhibition of JAK1 signalling is the best answer. This reduces intracellular signal transduction from several pro-inflammatory cytokines. PDE4 inhibition describes apremilast. Blockade of the IL-12/23 p40 subunit describes ustekinumab, whereas TNF-alpha blockade describes agents such as adalimumab. IL-17A inhibition is the mechanism of secukinumab and ixekizumab. Upadacitinib should not be interpreted as absolutely specific for JAK1; the SmPC describes preferential functional inhibition rather than exclusive activity.
Reference: Electronic Medicines Compendium, RINVOQ 15 mg prolonged-release tablets, Summary of Product Characteristics, section 5.1 Pharmacodynamic properties: Mechanism of action, text revised 4 June 2026. https://www.medicines.org.uk/emc/product/10972/smpc